1. Field of the Invention
This invention relates generally to video tape apparatus, for example, video tape recorders (VTR), and particularly to means for counting pulses related to the length of tape used to record a specific video signal interval, such counting means being responsive at least during Fast Forward and Rewind modes of operation to count previously recorded tape synchronizing pulses.
2. The Prior Art
Video tape apparatus recording or reproducing video signals has been designed to be used with cassettes in which the tape is wound on one or more reels contained in a housing. When video signals are to be recorded on, or reproduced from, the tape by means of the apparatus, a cassette is placed in the apparatus in an operative position in which rotatable members extend through respective apertures in the cassette housing and engage the reels therein. The apparatus also includes magnetic heads, or transducers, which are usually rotatably associated with a guide drum mounted on the chassis of the apparatus and spaced from the cassette when the latter is in its operative position. A tape loading device is provided for engaging the tape still within the cassette housing and withdrawing a loop of the tape from the housing and wrapping the withdrawn loop about a portion of the guide drum to be scanned by the rotary magnetic heads along oblique, or skewed, tracks on the tape.
One example of such apparatus is disclosed in detail in U.S. Pat. Ser. No. 3,740,495. In such automatic tape loading and unloading apparatus, a rotatable support member in the form of a ring encircles the rotary guide drum and carries a number of tape guide that define an arcuate tape guide path spaced from the drum. A tape engaging member is also mounted on the rotatable support member and is movable with respect to the latter into and out of the arcuate guide path. In an inactive, or starting, condition of the device, the tape engaging member is displaced out of the guide path so as to engage the tape between the take-up and supply reels of the cassette. The tape engaging member is then moved into the guide path in response to rotation of the support member during the loading operation to draw a loop of tape from one or both of the reels and to wrap one side of the loop about the guide drum while the tape guides move into the loop and engage the other side of the loop to maintain the latter side spaced from the surface of the guide drum. During the tape unloading operation in which the loop is allowed to retract back into the cassette, the tape engaging member remains in the guide path during the major portion of its movement with the rotatable support member for unwrapping the tape from around the guide drum and, at the conclusion of the tape unloading operation, the tape engaging member is moved out of the guide path so as to permit the loop of tape to be rewound on one or both of the reels.
In still another previously proposed automatic tape loading and unloading device disclosed in U.S. Pat. application Ser. No. 354,992, filed Apr. 27, 1973, now U.S. Pat. No. 3,821,805 and having a common assignee herewith, the support ring is turnable around the guide drum along an arcuate path that extends under the cassette when the latter is in its operative position. A tape engaging assembly that includes a pinch roller is carried by the support ring and extends into an opening of the cassette for engagement with the tape therein when the ring is in an inactive or starting, position. The tape engaging assembly draws a loop of the tape from the cassette and wraps one side of the loop part of the way around the guide drum and between the pinch roller and a capstan that is positioned to be adjacent the location of the pinch roller after the ring has turned to its operative position during the tape loading operation. A tape guiding member mounted on the support ring and a separate, pivotally mounted tape guiding member are moved from respective inner positions, at which these members extend into the cassette opening when the support ring is at its starting position, to respective outer positions during the loading operation, whereby these tape guiding members wrap one side of the loop part way around the drum and hold the other side of the tape loop away from the guide drum.
Related apparatus is also shown in U.S. Pat. application Ser. No. 399,049, filed Sept. 20, 1973, now U.S. Pat. No. 3,869,099, and U.S. Pat. application Ser. No. 415,220, filed Nov. 12, 1973, both assigned to the same assignee as the present application.
In all of the existing apparatus, the tape is withdrawn from the cassette as a loop that is brought around the guide drum and into the position for either recording or playing back video signals. When the tape is to be rewound at high speed from the take-up reel to the supply reel or is to be moved forward at high speed, it is entirely returned to the cassette for the high speed operations. One disadvantage of doing this is that the tape does not move past any head that could pick up signals. Also, the reels may not be on the same level and, if not, there is a tendency for the edge of the tape to rub against the flanges of the reels and thereby stretch the tape nonuniformly.
An important use of video tape apparatus and the like is in editing tape. If a scene, or batch of information, is to be added to an existing tape or to be deleted from the tape without leaving an area in which there is no signal, it is common to transfer the recorded information from one tape to another. This requires that the tape be played up to the point where the change is to take place and then be stopped. Even if it is known that the change is to take place at some specific point in the recorded video signal, for example 23 minutes and 15 seconds after the beginning of the tape, it is difficult to move the tape to that position without playing out all of the 23 minutes and 15 seconds in the Playback mode of operation and then stopping the tape. When the tape is entirely within the cassette during the Fast Forward mode or the Rewind mode there has heretofore been no way of knowing how much tape has been transferred from one reel to the other except by rough guess.